In general, fish paste products are produced by adding sodium chloride to ground fish meat, mixing it with stirring (so-called “shio-zuri”), adding seasonings, starch, water, etc. thereto, molding the resulting mixture and then elevating the temperature. The ground fish meats employed as the starting materials are usually stored and transported in a frozen state and widely utilized as materials for producing various food products.
Fishes processed into ground fish meats are exemplified by croaker (Nibea mitsukuri), swordfish (Makaira mazara), sand borer (Argentina semifasciatus KISHINOUE), lizardfish (Saurida undosquamis), warazuka (Stichaeus grigorjewi HERZENSTEIN) and Alaska pollack (Theragra chalcogramma). In recent years, Alaska pollack, etc. have been mainly employed therefor because of the decrease in the trawl fishery catch. However, pollacks are liable to be denatured in meat qualities during the freezing step. Thus, it has been a practice to add about 5% of sugar to frozen ground fish meat for preventing the denaturation and, at the same time, to thoroughly leach the ground fish meat with water so as to eliminate water-soluble enzyme proteins and salts, which participate in the denaturation during freezing, therefrom.
Frozen ground fish meat is produced via the following steps. First, the fishes are washed. After removing the heads and internals, the fishes are washed again and the meat is collected therefrom. The fish meat thus collected is next leached with 4 to 5 times as much water so that water-soluble proteins and salts are eliminated therefrom as far as possible. Subsequently, the fish meat is pressed, dehydrated and strained. After adding 5 to 10% of sugar and 0.2% of polyphosphates, the obtained blend is well mixed. 10 kg of this mixture is packed in a polyethylene film and rapidly frozen at about −35° C. with the use of a contact freezer to thereby give frozen ground fish meat. The frozen ground fish meat is stored usually at −15 to −25° C.
To produce fish paste products with the use of the frozen ground fish meat thus obtained, the frozen ground fish meat should be thawed and then subjected to shio-zuri. Known methods for thawing include spontaneous thawing, high frequency thawing, pressurized thawing in the presence of salt, etc. However, the frozen ground fish meat is in the form of a frozen pan weighing 10 kg and thus cannot be easily thawed. Thus, it is unavoidable that the frozen ground fish meat is thawed unevenly even though a thawing apparatus is employed, which brings about a problem that the ground fish meat sensitive to temperature is partly deteriorated in the qualities. Such deterioration worsens and, in its turn, makes unstable the qualities of the fish paste products.